Recently, various driving assistance systems become available. For instance, Patent Document 1 describes a driving assistance system that computes a degree of driving behavior risk by using a gaze of a driver.
Patent Document 1: JP-2003-99899 A
In detail, in a first system in Patent Document 1, a computation unit for a degree of driving behavior risk determines a traveling direction of a subject vehicle based on steering angles detected by a steering angle sensor. Further, this unit computes the risk degree by checking how long or how frequent the driver sees the traveling direction from a given time point before to the present time using behavior of the driver's gaze grouped with a gaze filter. For instance, the driving behavior risk decreases when the driver sees the traveling direction more than a given threshold period or more than a given threshold frequency. In contrast, the risk increases when the driver does not see the traveling direction more than a given threshold period or more than a given threshold frequency.
Further, in a second system in Patent Document 1, a computation unit for a degree of driving behavior risk determines whether a driver's gaze is on an object that is obtained from photographing images outside the vehicle and should be recognized by the driver. The computation unit then computes the risk degree by considering various parameters. For instance, the driving behavior risk decreases when the driver's gaze is on a bicycle approaching the subject vehicle, while the risk increases when the gaze is not on the bicycle.
In the above first system, whether a driver sees the traveling direction is determined based on not only the driver's visual behavior at the present time but also that in the past. In contrast, in the second system, the degree of the driving behavior risk is determined without considering the visual behavior in the past. In general, a person's visual memory remains for a given period. Suppose a case that a driver does not see an object at a moment when the degree of the risk is determined. Even in this case, the risk degree often decreases if the driver saw the object just before the moment. In contrast, continuing observing the object based on the instruction of the system may cause a secondary risk.